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pot are dropped into the retort, the tubulus of which is closed
with a cork holding a thermometer. Before commencing the
distillation the apparatus should be tested to see that it is air-
tight. It [Lis then evacuated with the water pump (See Fig. 35,
p. 44), and the distillation commenced.
During the distillation it is advisable
to hold the Bunsen and to heat the
retort with the bare flame. Under a
pressure of 36 mm. the acid distils at
245°. The pale yellow oil which col-
lects in the receiver is poured out
into a basin whilst hot and allowed to
cool. The cake of acid is spread on
a porous plate and left to drain,
when it becomes nearly colourless,
and, after one or two crystallisations

from   small   quantities  of   spirit, is  pure,   and  melts at 62°.
Yield about 20 grams.

The aqueous portion from which the cake of acid is removed
contains free hydrochloric acid, potassium chloride, andglycerol.
The latter may be obtained by evaporating to dryness on the
water-bath, and extracting the residue with small quantities of
alcohol, which dissolves out the glycerol. On evaporating the
alcohol impure glycerol is left.

FIG. 67.


CH.O.COCnH3l +

Palm i tin.

3C16HS1COOK + C3>H6(OH)3

Potassium palmhate.         Glycerol.

C16H31COOK + HC1 = C15H31COOH + KC1.
Properties.—Crystallises in tufts of colourless needles ; m. p.
62° ; soluble in alcohol and ether ; insoluble in water.
Reactions.—i. Dissolve a small quantity of the acid in caustic
soda solution and add salt. Sodium palmitate separates as a
curdy white precipitate.
2. Boil another portion of the acid with caustic soda and let it
cool Pour off the liquid from the crust of sodium palmi-
tate, which forms on the surface, wash once or twice with